In fuel injection systems for internal combustion engines, especially of the multipoint type, it is known that, for each cylinder of an engine, at least one injector delivers fuel to the corresponding branch of the inlet manifold. The inlet manifold being located directly upstream from the corresponding inlet valve(s), in the cylinder head of the engine. A butterfly valve body provides and regulates the air supply to the inlet manifold and, thus, to the engine located between the air filter and the inlet manifold, and having at least one duct therethrough. A throttle member in the form of a disk, called a butterfly valve, is mounted rotatably in the duct. The throttle member's position in the duct varies between a fully open position and a position in which the duct is more or less completely closed, depending on the position of the accelerator pedal and possibly on certain operating parameters of the engine.
The fuel atomization provided by the injectors may be improved by piercing the tip of an injector by at least one fuel outlet passage, defining a mixing chamber connected to an inlet for assisting air (U.S. Pat. No. 4,957,241). A three-port solenoid valve which regulates idling may also be used to draw off the flow of additional air supplied to each air-assisted injector (U.S. Pat. No. 5,048,496).
Fuel injection devices are also known in which the butterfly valve can close the inlet duct practically completely. The body of the butterfly valve includes an additional air duct whose inlet is located upstream from the butterfly valve and whose outlet is located downstream therefrom, and in which a solenoid valve controls the flow. Operating parameters of the engine control the solenoid valve. For example, the opening of the butterfly valve and speed of the engine regulate the idling speed and the water temperature and also the speed of the engine for cold starting. Reduction of pollution from exhaust gases during cold starting and when decelerating from high speeds as well as regulating of idling is thus possible.
French patent application FR 2 698 128 proposed an additional air duct, whose inlet is located upstream from the butterfly valve and whose flow can be controlled by a solenoid valve. This additional air duct ensures better fuel atomization when the engine operates in modes other than full load, especially when starting at a very low temperature (cold running), when decelerating from high speed and when running with a reduced load. The additional air duct feeds the air that has passed through the additional air solenoid valve to the mixing chamber of each of the air-assisted injectors and to a supplementary solenoid valve opening downstream from the butterfly valve.
In order to avoid the need to control two solenoid valves, which requires two actuators and complicates implementation of the control circuit, a two-stage valve has been proposed. The two-stage valve comprises a body having a moving assembly comprising first and second pistons, returned by resilient means to a position of sealed contact or of contact with minimum leakage against first and second seats respectively. This minimizes communication between at least one inlet in the body, fed with air from upstream of the throttle member, and respective ones of two outlets of the body, a first feeding the air-assisted injector(s), and the second feeding the manifold downstream from the throttle member. In order to place each outlet progressively in communication with the corresponding inlet, an actuator moves the moving assembly against the return of resilient return means by spacing the corresponding piston from its corresponding seat.
However, that implementation suffers from the problem that the two pistons are integral with a member controlled by an actuator, so that they are moved simultaneously relative to their respective seats. This precludes control and regulation of the airflow through one of the two outlets of the valve unless the airflow through the other is controlled and regulated.
However, the requirements for a regulated supply of additional air firstly to the air-assisted injectors and secondly to the inlet manifold, bypassing the butterfly valve, are not simultaneous.